Sometimes people refer to how much electrical power a power generator is currently generating, but not in units of power (such as Watts), but as a percentage of its maximum capability.

The first example that comes to mind is from the movie The Hunt for Red October, where a submarine captain who needs to get somewhere in a hurry asks about "going to 105 [percent] on the reactor," i.e. he wants to run the generator at 105% of its... design-maximum something so he can travel faster than the sub's normal maximum speed.

This kind of thing comes up in other fiction, especially Star Trek. But since the context provides so much, the language used (whether dialogue or narration) always seems to omit the specific term for whatever property or setting this is. The example above seems typical.

The only word I've ever heard with any consistency is "level," as in "what's the reactor level?", but it seems pretty clear to me that this is also just conversational shorthand, since it clearly omits some phrase that identifies which level.

It is irrelevant to me whether a change to this performance characteristic is accomplished by turning a single knob vs adjusting very many settings in concert. I'm looking for the term that refers to the observable outcome, not the names of the pieces of machinery that must be adjusted.

What is the correct, precise term that unambiguously for this performance characteristic?

In other words: if a nuclear reactor had a gauge that showed this value, how would it be labeled? (That is my actual use-case: I need to label a readout.)

  • It’s whatever the meter displays. Power, RPM, amps, Volts, watts, fuel flow. And sometimes the nominal value isn’t even 100%. On the AH-64 Apache the nominal power turbine RPM is 101%.
    – Jim
    May 2 at 4:42
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    Labeling things is off topic here. And there isn't really a term for this that works as a label. The type is referred to as percent full scale "In analog systems, full scale may be defined by the maximum voltage available, or the maximum deflection (full scale deflection or FSD) or indication of an analog instrument such as a moving coil meter or galvanometer." That is how I would describe the type of indicator on an equipment specification. But the indicator would be labeled "power" or whatever.
    – Phil Sweet
    May 2 at 9:21
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    You might refer to rated capacity, or rated x, whatever that is. May 2 at 10:21
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    Pretty often in fiction, it's just a made up percentage. This is for fiction, right? (If not I'm concerned that you're asking here instead of going to someone who's familiar with the equipment.)
    – Laurel
    May 2 at 14:38
  • @PhilSweet "What should I label my variable" is indeed off-topic. However, "what is this thing called" is very close to a single word request. In addition, "Full Scale" is the incorrect terminology. It refers to wave for amplitudes and AD converters not gauges. Lastly, if you have an answer to the question, do not put it in a comment. Post it as an answer.
    – TsSkTo
    May 6 at 16:27

2 Answers 2


From Law Insider

Maximum design capacity

Maximum design capacity means, in reference to a source operation, its maximum capability, per period of time, to operate, to consume a process input or to generate a product. This term may be expressed in units such as the maximum number of kilowatt-hours of electricity that a combustion unit is capable of producing per hour or the maximum amount of a raw material that may be processed per day.

It is possible to substitute "limit"/"output"/power/heat, etc. for "capacity" depending up the context.

Maximum design capacity is usually set somewhat below failure level.

  • OP specifies 'as a percentage of its maximum capability' where perhaps 'a change to this performance characteristic is accomplished by turning a single knob' (eg from the 60% to 75% 'level'). May 2 at 16:42

Your gauge will be labeled Power Output and will be measured in (Joules per second) Watts.

At 100 percent your generator will be providing its max safe power output. At 110 percent, your cooling system will be pushed to the limits alongside other components that had some redundancy built in to them.

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